Most likely two bugs. The bracket one, and the fact that sizeof(buffer) will give you the pointer size, not the buffer size if buffer is a pointer rather than an array.
The second one could only arise with unsafe pointers in Rust, as safe code uses slices, combining the base pointer and the element count in a single value.
OTOH the point here is to pass a preallocated but "uninitialised" buffer to the callee, which Rust wouldn't allow with slices, unless you created a slice from a raw allocation (I don't know if that's defined behaviour, though I guess you could do that safely by passing in a Write rather than the slice itself, but then you're Write-ing to a slice which has… interesting behaviour)
#include <stdio.h>
static char buffer[80];
static char *bufferp=buffer;
int main(int argc, char *argv[] )
{
char localbuffer[80];
char *localbufferp=localbuffer;
printf("buffer: %ld\n",sizeof buffer);
printf("bufferp: %ld\n",sizeof bufferp);
printf("localbuffer: %ld\n",sizeof localbuffer);
printf("localbufferp: %ld\n",sizeof localbufferp);
}
marcel@sarek[tmp]./a.out
buffer: 80
bufferp: 8
localbuffer: 80
localbufferp: 8